1. Field of the Invention
The present invention relates to a vehicle in which a torque generated in an engine is transmitted to driven wheels through a torque converter and an automatic transmission, and particularly, to a process for estimating such a drive torque.
2. Description of the Related Art
A technique for estimating a drive torque transmitted from an engine through an torque converter and an automatic transmission to driven wheels in a vehicle including a torque converter is known from Japanese Patent Application Laid-open No.10-181564, which technique comprises multiplying an engine torque (torque input to the torque converter) by a torque ratio of the torque converter to calculate a torque output from the torque converter, and multiplying the torque output from the torque converter by a gear ratio of the transmission to calculate a drive torque.
Another example of the above-described technique for estimating a drive torque is known from Japanese Patent Application No.11-256831, which technique comprises multiplying a vehicle body acceleration resulting from the time-differentiation of a wheel speed by a vehicle body mass to calculate a vehicle body-driving force, and multiplying the vehicle body-driving force by a dynamic load radius to estimate a drive torque.
The former technique suffers from a problem that in a region in which a speed ratio in the torque converter is smaller (namely, in a region in which the slipping of the torque converter is larger), the accuracy of estimation of the drive torque is reduced due to a time lag till the transmission of the engine torque to the driven wheels. The latter technique suffers from a problem that the accuracy of estimation of the drive torque is reduced, because the vehicle body acceleration is influenced by a gravity acceleration during traveling of the vehicle up and down a slope.
Accordingly, it is an object of the present invention to ensure that a correct drive torque can be always estimated irrespective of an operational state of the engine and an operational state of the vehicle.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided a process for estimating a drive torque in a vehicle in which a torque generated in an engine is transmitted to driven wheels through a torque converter and an automatic transmission, the process comprising the step of multiplying an estimated engine torque Ti by a torque ratio k of the torque converter to estimate a drive torque Td, when a speed ratio e in the torque converter is equal to or larger than a predetermined value, and estimating a drive torque Td from an engine rotational speed Ne and the speed ratio e in the torque converter, when the speed ratio e in the torque converter is smaller than the predetermined value.
With the above feature, when the speed ratio e in the torque converter is equal to or larger than the predetermined value, and a capacity xcfx84 of the torque converter cannot be estimated accurately, the estimated engine torque is multiplied by the torque ratio k of the torque converter to estimate the drive torque Td. When the speed ratio e in the torque converter is smaller than the predetermined value, and the rising of the engine torque is earlier than the rising of the drive torque Ts, the drive torque Td is estimated from the engine rotational speed Ne and the sped ratio e in the torque converter. Therefore, a correct drive torque can be always estimated irrespective of the magnitude of the speed ratio e in the torque converter.
According to a second aspect and feature of the present invention, in addition to the first feature, there is provided a process for estimating a drive torque in a vehicle in which, when the speed ratio e in the torque converter is equal to or larger than the predetermined value, the torque ratio k of the torque converter is calculated from the speed ratio e in the torque converter, and the estimated engine torque Ti is multiplied by the torque ratio k of the torque converter to estimate the drive torque Td.
With the above feature, when the speed ratio e in the torque converter is equal to or larger than the predetermined value, and the capacity xcfx84 of the torque converter cannot be estimated accurately, the torque ratio k of the torque converter is calculated from the speed ratio e in the torque converter, and the estimated engine torque Ti is multiplied by the torque ratio k of the torque converter to estimate the drive torque Td. Therefore, the drive torque Td can be estimated correctly.
According to a third aspect and feature of the present invention, in addition to the first feature, when the speed ratio e in the torque converter is smaller than the predetermined value, the torque Ti input to the torque converter is calculated from the engine rotational speed Ne and the capacity xcfx84 of the torque converter, the torque ratio k of the torque converter is calculated from the speed ratio e in the torque converter, and the torque Ti input to the torque converter is multiplied by the torque ratio k of the torque converter to estimate the drive torque Td.
With the above feature, when the speed ratio e in the torque converter is smaller than the predetermined value, and the rising of the engine torque is earlier than the rising of the drive torque Td, the torque Ti input to the torque converter is calculated from the engine rotational speed Ne and the capacity xcfx84 of the torque converter; the torque ratio k of the torque converter is calculated from the speed ratio e in the torque converter, and the torque Ti input to the torque converter is multiplied by the torque ratio k of the torque converter to estimate the drive torque Td. Therefore, the drive torque Td can be estimated correctly.
According to a fourth aspect and feature of the present invention, in addition to any of the first, second and third features, the predetermined value of the speed ratio e in the torque converter is 0.85.
With the above feature, techniques for estimating the drive torque Td is changed from one to the other between when the speed ratio e in the torque converter is equal to or larger than 0.85 and when the speed ratio e in the torque converter is smaller than 0.85. Therefore, the drive torque Td can be estimated correctly over a wide range of the speed ratio e.
According to a fifth aspect and feature of the present invention, in addition to the first feature, during shifting of the automatic transmission, the drive torque Td is estimated from a vehicle speed V.
With the above feature, during the shifting of the automatic transmission in which the driven wheels are disconnected from the engine and the torque converter, the drive torque Td is estimated from the wheel speed V. Therefore, even if neither of the engine torque-based method nor the torque converter-based method can be used, the drive torque can be estimated.
According to a sixth aspect and feature of the present invention, in addition to any of the first to fifth features, the estimated drive torque Td is used to calculate a drive distribution torque between the left and right driven wheels.
With the above feature, the drive distribution torque between the left and right driven wheels is calculated based on the estimated drive torque Td, and hence, it can be calculated accurately.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.